1. Field of the Invention
The present invention relates to a data communication unit for use in mobile radio such as that in automobiles, and more particularly to a communication system with use of a block synchronization signal.
2. Description of the Prior Art
A mobile phone system is now commercially available in Japan, Canada, and various countries in Europe, the United State of America, but data communication with mobile radio has, at long last, begun to be put into a practical use. The data communication with mobile radio is mediated through a transmission channel under a severe handicap such as fading. Thus, such data communication may suffer from errors. To solve the problem, the data in question is commonly subjected to error correction encoding and is blocked for transmission. A communication system of such types of error correction is called a block synchronization transmission system in which block data signal. Many methods have been proposed up to now for such systems. An example is described in "Computer-Data communication Techniques"--The Elements In Data Communication--, written by E. Macnamara, translated by Hiroyuki Watanabe from CQ Publishing Co., Ltd., PP 138 to 141, wherein two methods are given. One of them a block synchronization signal with a single pattern having an arbitrary bit length and employs it one at a time for transmission. The other transmits the pattern three times or more in repetition and identifies it as being a proper block synchronization signal provided that it is received two times or more in succession. In addition, another technique is given in "Advanced Mobile Phone Service: Control Architecture" by Z. C. Fluhr et al, THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1979, which describes a data format in data communication (P58, FIGS. 8 and 9). However, only with a single pattern, it is not recognized as a block synchronization if it is received by mistake. Likewise, with a single pattern transmitted in a plurality of times, it can be not decided with ease from which portion a data fraction begins in the signal if the pattern is received by mistake.